1. Field of the Invention
The present invention is directed to the preparation of 4,4'-dihydroxybiphenyl. More particularly, this invention involves the hydrolysis of 4,4'-dibromobiphenyl in the presence of a copper compound catalyst. A mixed solvent system is used to recover pure 4,4'-dihydroxybiphenyl from the crude product.
2. Description of the Prior Art
4,4'-Dihydroxybiphenyl is useful as an antioxidant for a resin, an intermediate for a dye and a starting material for polyesters, polyepoxides, polyurethanes and polycarbonates. It may also be used as a co-monomer in high performance polyester film, cable, rope and engineering plastics.
U.S. Pat. No. 4,340,768 teaches the production of 4,4'-dihydroxybiphenyl by hydrolyzing 4,4'-dibromobiphenyl in the presence of a copper compound catalyst in an aqueous solution, extracting by-products from the alkaline aqueous solution with an alcohol or ketone which forms an organic phase, neutralizing or acidifying the alkaline aqueous solution with an acid, extracting the reaction product with the alcohol or ketone and finally crystallizing the reaction product from the extracted solution. This process requires two extractions using an alcohol or ketone. The first extraction is designed to remove by-product impurities.
Copending application U.S. Ser. No. 469,724, filed Feb. 25, 1983 describes a process for preparing 4,4'-dihydroxybiphenyl. However, a rather lengthy process is used to recover pure 4,4'-dihydroxybiphenyl from the crude product. After the acidification and separation to obtain the crude product, the solid crude product was then dissolved in an inert organic solvent leaving an inorganic salt residue. The salt residue was separated and removed. An aromatic hydrocarbon such as toluene may be added to this solution to azeotrope out residual water during the distillation to produce a dry product. Unfortunately, the quality of the product obtained in this manner was oftentimes quite crude and further recrystallization or purification was therefore necessary.
It has now been discovered that immediately after the acidification and separation to obtain a crude product, a relatively pure product can readily be obtained using water and an inert organic solvent in which the 4,4'-dihydroxybiphenyl (biphenol) is soluble.